1. Field of the Invention
The present invention relates to an optical recording medium in which information is recorded in the direction of depth of the substrate, and a method and apparatus of reproducing information therefrom. More particularly, the present invention relates to a read only or recordable optical recording medium including a first region in which first information such as additional information is recorded at least in the depth direction of the substrate and a second region in which second information such as main information is recorded or can be recorded in the plane direction of the substrate, and a reproduction method and reproduction apparatus of such an optical recording medium.
2. Description of the Background Art
In a conventional optical recording medium such as an optical disk, binary recording is carried out, wherein information is binarized and recorded corresponding to the presence/absence, the length, the width, or the position in the substrate plane of pits, marks and the like. More specifically, pits are provided on the substrate in a read only optical disk (referred to as ROM disk hereinafter) to have information recorded. In contrast, recording marks are provided at the recording layer on the substrate in a recordable disk such as a phase change disk, magneto-optical disk, and organic dye disk to have information recorded.
Information is transposed to the absence/presence, the length, the width, or the position in-the substrate plane of pits, marks or the like to be recorded on an optical disk. In other words, information is recorded in the dimension of the plane direction of the substrate using pits, marks and the like. The string of pits, marks, or the like is arranged concentrically or spirally on a circular substrate to form a track. The light beam for reproduction follows this track to scan the string of pits, marks or the like. Taking advantage of the change in the quantity of reflected light, rotation of the plane of polarization of light and the like based on these pits and marks, recorded information is reproduced.
The pit string, mark string and the like formed concentrically or spirally are generally assigned an address sequentially from the inner circumference towards the outer circumference. A predetermined region at the inner circumference side with the smaller address constitutes the region generally called “lead-in”. Information unique to the relevant optical disk is written in this lead-in region. More specifically, various information required for the disk drive, disk player, disk recorder or the like to record information or reproduce information to/from the optical disk is written in the lead-in region.
Information unique to the disk includes, for example, information identifying the disk type (ROM disk, R disk, RW disk, RAM disk, or the like), information specifying the rotation speed and linear velocity of the disk for recording and reproduction, the laser power during recording or the like, the address information of a region on the disk that can be used by the user, key information required to cancel the scramble or encryption, and the like.
The key required to descramble or decrypt is the key used in scrambling or encrypting the contents. The scramble or encryption cannot be canceled without this key. In other words, this release key is indispensable to reproduce the scrambled or encrypted contents.
In accordance with the higher density and higher level of functions of disks, the trend is to increase the amount of information written in the lead-in region.
A conventional optical recording medium and a reproduction method and apparatus of an optical recording medium will be described hereinafter with reference to the drawings.
FIGS. 6-8 show a first example of a conventional optical recording medium. FIG. 6 schematically shows the arrangement of pits formed on a ROM disk as an example of an optical recording medium. A pit string 33 of a plurality of pits 32 are formed spirally on the plane of a substrate 31, whereby information is recorded.
FIG. 7A is a schematic representation of pit string 33 formed spirally in the conventional ROM disk of FIG. 6, illustrated in a linear version from the inner circumference region to the outer circumference region of substrate 31. The lead-in region is provided at the inner circumference side of the disk, and the user region is provided at its outer circumference side.
The ROM disk ID (identification information), the address information of the user region and the like are recorded in the lead-in region. When the information written in the user region is scrambled or encrypted, a scramble key or encryption key thereof is also recorded in this lead-in region.
Main information such as video and audio data is recorded in the user region. When the contents become the subject of copyright protection, the main information will be recorded in a scrambled or encrypted manner.
FIG. 7B is a schematic sectional representation of substrate 31 corresponding to pit string 33 of FIG. 7A. The portion of pit 32 is represented as a hole. Pit 32 is formed with a constant depth.
FIG. 7C shows an RF signal representing the quantity of reflected light obtained by reproducing pit string 33 with a reproduction light beam (not shown). FIG. 7D represents a tangential push-pull signal (TPP signal) obtained by reproducing pit string 33.
The RF signal and TPP signal will be described hereinafter with reference to FIGS. 7C, 7D and FIGS. 8A and 8B. FIG. 8A schematically shows the scanning manner of a beam spot 34 of the light beam for reproduction on pit 32. FIG. 8B schematically shows the manner of reflected light 35 of the reproduction light beam from the disk plane entering photoreceptor elements 36a and 36b forming a detector 37 that is divided into two regions, region A and region B. The RF signal and TPP signal are obtained by the following equations using respective outputs A and B of photoreceptor elements 36a and 36b. RF=A+B TPP=A−B 
An RF signal having a waveform as shown in FIG. 7C is obtained since the quantity of reflected light of the light beam is small at the pit portion and large at the non-pit portion. Also, since the pit is formed with a constant depth, a TPP signal as shown in FIG. 7D that changes with the same polarity will be obtained with respect to all pits, as will be described afterwards.
FIGS. 11A and 11B schematically show a structure of a string of marks in a recordable disk which is a second example of a conventional optical recording medium. FIGS. 11C and 11D represent the waveforms of respective signals obtained by reproducing information from the recordable disk.
FIG. 11A schematically shows a mark string 46 formed of a number of marks 45 written on the plane of a recordable disk, illustrated in a linear version from the inner circumference region to the outer circumference region of a substrate 41. A guide groove of the light beam that is generally referred to as a groove is provided in the recordable disk. The light beam for recording follows this groove 44 or the land which is a region between grooves to write a mark 45. Mark 45 can be written in either or both of the groove and land. FIG. 11A shows an example of marks 45 written in groove 44.
FIG. 11B schematically shows a cross section of the disk, corresponding to mark string 46 of FIG. 11A. It is appreciated from FIG. 11B that the mark portion is provided so that the reflectance of light differs between a mark portion 45 and a non-mark portion 48 in a recording layer 47 provided on substrate 41, and not formed as a hole such as for the pit.
FIG. 11C shows an RF signal representing the quantity of reflected light obtained by reproducing mark string 46 with a reproduction light beam. The quantity of reflected light is smaller in mark portion 45 than in non-mark portion 48.
FIG. 11D represents a TPP signal obtained by reproducing mark string 46. Since mark 45 is formed with a constant depth in groove 44, a TPP signal that changes with the same polarity is obtained from all marks 45.
FIGS. 12 and 13A-13D show a third example of a conventional optical recording medium. FIG. 12 schematically shows a recordable disk that employs a phase change recording layer in an unrecorded status as an example of an optical recording medium. A groove 54 which is a guide groove is formed spirally on the plane of a substrate 51. Information is recorded in the form of marks in groove 54. Pits 52 are formed instead of groove 54 at the inner circumference side of the disk. Information that should not be rewritten is recorded by pits 52.
FIGS. 13A and 13B schematically show the structure of a mark string and pit string of the recordable disk of FIG. 12. FIGS. 13C and 13D represent the waveforms of respective signals obtained by reproducing recorded information from the recordable disk.
FIG. 13A schematically shows a mark string 56 formed of marks 55 recorded on a spiral groove 54 and a pit string 53 formed of pits 52 in the recordable disk, illustrated in a linear version from the inner circumference region to the outer circumference region of substrate 51. It is to be particularly noted that marks 53 and pits 52 are aligned in the lead-in region.
Mark 55 can be written in either or both of the groove and land. In the example of FIG. 13A, marks 55 are written in groove 54. The lead-in region is provided at the inner circumference side of the disk, and the user region is provided at its outer circumference side. In the lead-in region, recorded are the disk ID (identification information), the address information of the user region, and the scramble key or encryption key in the case where the information written in the user region is scrambled or encrypted.
The user region is recorded with main information such as video and audio data. When the contents are copyrighted, the main information is recorded in a scrambled or encrypted manner.
FIG. 13B schematically shows the cross section of the disk corresponding to mark string 56 and pit string 53 of FIG. 13A. Pit 52 is formed as a hole with a constant depth. In contrast to the formation of a hole as for pit 52, mark 55 is provided so that the reflectance of light differs between a mark portion 55 and a non-mark portion 58 in a recording layer 57 provided on substrate 51.
Although the depths of groove 54 and pit 52 may be identical, it is preferable for a shallower groove 54 for the purpose of improving the signal quality of mark 55. If the signal quality of pit 52 is to be set more favorable, a depth of approximately λ/4n is preferable, as will be described afterwards. Therefore, it is preferable to form the pit deeper than the groove. Here, λ is the wavelength of light, and n is the refractive index of the disk substrate.
FIG. 13C shows an RF signal representing the quantity of reflected light obtained by reproducing mark string 56 and pit string 53 with a reproduction light beam. FIG. 13C corresponds to the case where the reflectance of mark portion 55 is smaller than the reflectance of non-mark portion 58.
FIG. 13D represents a TPP signal obtained by reproducing mark string 56 and pit string 53. Since mark 55 in groove 54 as well as pit 52 are formed with the same constant depth, a TPP signal that changes with the same polarity can be obtained from any mark and pit.
In the present third conventional example, the relationship between pit 52 and the beam spot is similar to that of the first conventional example shown in FIGS. 8A and 8B. Therefore, the RF signal and TPP signal are obtained by the following equations using respective outputs A and B of photoreceptor elements 36a and 36b of detector 37.RF=A+B TPP=A−B 
An RF signal as shown in FIG. 13C is obtained since the quantity of reflected light of the light beam is small at the pit portion and large at the non-pit portion whereas the reflectance is small at the mark portion and large at the non-mark portion. Referring to FIG. 13D, a TPP signal that changes at the same polarity from any pit can be obtained as will be described afterwards since pits 52 are formed with the constant depth. The TPP signal obtained from the mark portion and the TPP signal obtained from the pit portion have the same polarity.
In the above-described conventional ROM disk, a greater capacity (larger region) is required for the lead-in region as the amount of information written in the lead-in region increases. There was a problem that the region where user data can be recorded on the disk is reduced. Similarly in the above-described conventional recordable disk, a greater capacity larger region) is required for the lead-in region as the amount of information written in the lead-in region increases. There was a problem that the region where the user can write data on the disk is reduced.
From the standpoint of copyright protection, it is not desirable for the information in a ROM disk recorded with copyrighted contents to be easily copied to another recordable disk. However, since the conventional ROM disk has information recorded in the dimension of the plane direction of the substrate using pits, it is theoretically possible to copy the information in a ROM disk to another recordable disk. The role of copyright protection is low. Similarly in a conventional recordable disk, information in the recordable disk can be easily copied to another recordable disk in theory since information is recorded in the dimension of the plane direction of the substrate using pits, marks, and the like. The role of copyright protection is low.